A troiku is three haiku, with each of the three lines from a suggested haiku as the first line of each haiku in the troiku. It’s not always possible to have a 5-7-5 format in the second haiku, due to the limitations of the suggested haiku. The name of the form is derived from “troika,” a sled or carriage drawn by three horses harnessed side-by-side, an iconic symbol of Imperial Russia.